Headbutting behaviour between two males of the world's largest parrotfish species has been observed for the first time.
Dr Roland Muñoz of NOAA's Beaufort Laboratory and a team of researchers witnessed the behaviour while watching Green humphead parrotfish (Bolbometopon muricatum) at Wake Atoll in the North Pacific.
While observing the fish, the team heard loud jarring sounds and were surprised to discover that the noise was coming from the violent clashes between males as they crashed together, repeatedly headbutting one another.
"During headbutting bouts, males utilised their caudal fins to rapidly collide with their cephalic humps, immediately followed by fast swimming in a semicircle where each fish tried to bite the back and flank of its opponent," the scientists explain.
They also say that this is the first time such aggressive headbutting behaviour has been observed in marine fish.
Green humphead parrotfish, also known as Giant parrotfish, reach lengths of 1.5m/5' and can weigh as much as 70kg/154lb. They are the largest parrotfish species.
The research was published in the open-access journal PLoS-ONE.
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